Homework 3
Due Thursday, June 5


Directions for submission:  

   Make directories ProblemI and ProblemII, and put the relevant files
   in each:

      Problem I:  C source code and makefile; .tex and .eps (from
                  gnuplot) files for writeup of best backoff 
                  probability

      Problem II:  C source code and makefile

   Make a README file which gives the names of all people in your
   homework group.

   Use tar to combine README, ProblemI and ProblemII.  Then gzip and
   uuencode, and e-mail the result to the TA. 


I.  Modify the simulation in the handout, "Some Utilization Analyses
    for ALOHA and CSMA Protocols," so as to provide the following
    additional information:

       *  The average number of active nodes.

       *  The utilization of the channel.

       *  The average number of nodes involved in a collision.

    (You can print to stdout if you wish, in order to use the file as
    input to gnuplot.  By the way, please use the value 1000000 for
    NSLOTS.)

    Also, for NewMsgProb = 0.02 and NNodes = 16, experiment with
    different values of P to see the effects on utilization and mean
    delay, setting up two gnuplot graphs.  Explain the behavior you
    observe.

    To help check your work, here is what I got for P = 0.1:

       long-run average delay = 14.3
       mean number of active nodes = 3.6
       utilization = 0.25
       mean number of nodes in a collision = 2.1
 

II.  Write a program to input the Ethernet records in

        ~matloff/Pub/N*/E*/PktTrc01.dat

     The program will output the following:

        average received length of all Ethernet frames

	the number of ftp control frames (destination port 21, TCP)

	IP addresses (xxx.xxx.xxx.xxx format) and host names (use
           gethostbyaddr() for the latter) for source and destination 
	   in the first TCP frame, plus source and destination Ethernet 
	   board numbers (in hex) for that frame (note to yourself which 
	   machines we are talking about!)

     The relevant header formats are shown on pages 123, 221 and 291.
     Note that the Type code in an Ethernet frame for IP is 0x0800.

     Read the README file accompanying the data before starting.
     Make sure to browse through the data file (using od) "by hand" a
     bit first to get a feeling for the layout of the data, checking to
     see, for example, that there is always an 0x0800 code where it
     ought to be in the first two or three frames.